An antenna arrangement presently employed in communication technology includes a feed horn and one or mor associated reflectors. The term “feed horn,” as used herein, denotes an antenna capable of transmitting and/or receiving electromagnetic signals, for example, radio or microwave signals. The associated reflector(s) has a surface(s) typically described by rotating a conic sction, for example, a parabola, one full revolution to produce a dish-like surface.
FIG. 1 illustrates an antenna arrangement 100 in which a feed horn 104 is held in front of a reflector 108 by a plurality of spars 112. Feed horn 104 transmits and receives signals along an axis 116. Signals transmitted by feed horn 104 along axis 116 reflect against the surface 120 of reflector 108 en route to their destination. Signals arriving to antenna arrangement 100 reflect against surface 120 of reflector 108 and proceed along axis 116 to feed horn 104. In some usages, an antenna arrangement may be configured so that the feed horn only transmits or only receives signals.
FIG. 2 illustrates an alternate antenna arrangement 124 with two reflectors; a main reflector 128 and a sub-reflector 132. Signals transmitted by a feed horn 136 reflect first against a surface 140 or sub-reflector 132 and then against a surface 144 or main reflector 128 en route to their destination. Signals arriving to antenna arrangement 124 reflect first against surface 124 of main reflector 123 and then against surface 140 of sub-reflector 132 to feed horn 136.
Antenna arrangements 100 and 124 each individually forms “kits,” herein referred to as “dish antenna kits.” A dish antenna kit may include additional elements. For example, a dish antenna kit may have two feed horns: one feed horn for C-band operation (5.8 to 6.5 GHz.), and one feed horn for Ku-band operation (14 to 14.5 GHz.). The particular feed horn used depends on the needs of the user.
In some dish antenna kits, a relatively large reflector (or main reflector) may be formed as an assembly of a plurality of constituent panels. FIG. 3 illustrates a reflector 148 comprising four panels 152 joined at the edges to form seams 156. (Note that, although four panels are shown in this example, reflectors can have a different number of constituent panels.) Such a configuration permits convenient disassembly of the reflector and subsequent re-assembly of the reflector in the field. Sometimes, the term “fly-away kit” is used in reference to such a kit, due to the ease of disassembly and packaging as airline baggage to accompany the deployment personnel to a remote location to assemble the disk antenna kit.
Another type of dish antenna kit 160 adapted for mobility incorporates a trailer. As illustrated in FIG. 4, an antenna arrangement 162 including a feed horn 164 and a reflector 168 are mounted on a trailer 172. Also in this arrangement, a router 176 is housed inside an air-conditioned enclosure 180. Both the router 176 and the air conditioner of air-conditioned enclosure 180 are powered by a generator 184. To protect the router 176 from the vibrations caused by generator 184, shock attenuators 188 may be mounted between trailer 172 and enclosure 180. Accordingly, the dish antenna kit 160 may be conveniently towed to a remote location for use.
Whether in the field, the manufacturing facility, or elsewhere, the feed horn must be properly aligned with respect to the reflector(s) to optimize gain. The feed horn axis 116 (FIG. 1) desirably intersects with the reflector surface as close as possible to the surface's focus point. (The “focus point” is the point on the surface of the reflector for which the antenna gain is maximized if the feed horn axis intersects therewith.) The focus point of a reflector is often the center of the reflector's surface, although off-center focus points are sometimes desired.
Antenna arrangements in the field may also occasionally require realignment of the feed horns relative to the reflectors. Severe weather conditions or intrusive wildlife, such as spider monkeys, can misalign the antenna arrangements. Also, vibrations from generators, if part of the dish antenna kits, may require periodic realignment of the feed horns relative to the reflectors.
With limited success, various alignment tools have been proposed to facilitate the alignment procedure. For example, Burditt (U.S. Pat. No. 4,590,481) and Paullin (U.S. Pat. No. 4,608,573) disclose alignment tools that attach to a feed horn. “Telescoping” rods are extended to the reflector surface to indicate whether the feed horn axis intersects with the reflector surface at or near the focus point. These alignment tools require high precision manufacturing to ensure that the extended rods properly indicate where the feed horn axis intersects with the reflector surface.
Ehrenberg et al. (U.S. Pat. No. 6,466,175) discloses a dish antenna kit, and its FIGS. 24 and 25, with the corresponding text in the specification, illustrate a light source, sized and shaped for mounting in an antenna arrangement in place of the feed horn. A light beam projects upon the reflector surface to indicate whether the feed horn axis, after the feed horn later replaces the light source, will intersect with the reflector surface at the focus point. Such light source requires high precision manufacturing to ensure that its beam projects collinearly with the later position of the feed horn axis after the feed horn replaces the light source.
Ehrenberg et al. also provides a cursory statement (col. 18, lines 55–58) that a light source may be fashioned for attachment directly to the feed horn. However, no development of this idea accompanies the Ehrenberg et al. statement, so there is no guidance of how such an alignment tool can be created in such a way that it would not also require such high precision manufacturing in order to effect, correspondingly, high precision alignment.
To the present inventor's knowledge and belief, this aspect of Ehrenberg et al. has not been produced commercially and is not on the market.
Other procedures for aligning a feed horn relative to the reflector of an antenna arrangement are tedious and require multiple personnel using a variety of tools or implements (for example, tape measures, and mechanical gap gauges). An example of such a procedure is described in the Andrew installation guide. After following such procedures, uncertainty in proper alignment often remains due to the lack of a simple way to verify alignment.
Despite widespread use of lasers for alignment purposes (for example, installing dropped ceilings) no one, prior to the present inventor, has successfully adapted laser-alignment devices to the to the peculiar problems encountered in feed horn alignment for satellite antennas on the commercial market.
Accordingly, to the best knowledge of the present inventor, there remains a need for a dish antenna kit that includes an alignment tool, which is both easy to use and achieves highly precise alignment of the feed horn with respect to the reflector of the kit. Also, it is desirable that such an alignment tool provide the highly precise alignment without requiring manufacturing of as high precision and cost as that for the prior art discussed above.